The present invention relates in general to machinery useful in the manufacture of beer and beverage containers, and in particular, it relates to an improved system for the insertion of liquid nitrogen into such containers at the time they are filled.
In the beer and beverage container industry, metal containers having very thin sidewalls are especially desirable because the cost of the raw materials from which those containers are made may therefore be reduced. However, the sidewall thickness of beer and beverage containers may not be decreased without limit. If the sidewall of a beer and beverage container becomes too thin, the container does not have sufficient rigidity. Such a container may dent or crumple when proceeding through the liquid filling line of a brewer or bottler for insertion of the container contents. Also, when pallet loads of filled containers are stacked one upon another, for example, in a warehouse or during transport, damage to those containers near the bottom of the pallet loads may result.
Generally, in the past, thinner walled containers could be utilized for the packaging of beer and certain carbonated beverages than could be employed with certain low or non-carbonated beverages. Since beer and carbonated beverages develop an internal pressure, that pressure is utilized to prevent inward deformation of the very thin walled container during handling. However, in the case of non-carbonated beverages or beverages having a rather low carbonation, thicker walled containers have been utilized since the internal pressure of the beverage contents may not be relied upon to aid in the provision of structural rigidity to the container itself.
To solve the foregoing difficulty in the case of beverages having low or no carbonation, liquid nitrogen injection systems have been proposed. In such systems, small quantities of liquid nitrogen are inserted into the head space at the top of a filled container. Subsequent evaporation of the liquid nitrogen after the container is filled and closed simulates the internal pressure of beer and carbonated beverages and therefore permits the use of thinner walled containers than might otherwise be employed.
In one known liquid nitrogen injection system, as filled containers pass an orifice in a can filling line, a small quantity of liquid nitrogen is dispensed into such containers by means of the opening of a solenoid controlled valve. One problem associated with this nitrogen injection system resides in the fact that the solenoid operated valve for dispensing liquid nitrogen must open and close, i.e., recycle, once for each container passing the discharge orifice. Because the speed of a can filling line may be exceedingly high, sometimes on the order of 1200 containers per minute, problems with the solenoid valve may be experienced. Problems with the solenoid activated valve for insertion of liquid nitrogen into the container may cause one of two related problems. First, an excess amount of nitrogen may be injected into a container thereby causing the container to have more than a desired internal pressure when the liquid nitrogen is vaporized. Excess pressure may cause cans to rupture, thereby causing danger to the consumer. On the other hand, if insufficent nitrogen is injected, the internal pressures developed may not be adequate to prevent deformation of thin walled containers.
Still other problems associated with known nitrogen injection systems are noticeable when the speed of a can filling line fluctuates. In those systems, can sensors are provided which sense the presence or absence of cans passing a particular point in a can filling line. Electrical circuitry in response to those can sensors opens and closes a valve for the dispensation of liquid nitrogen at a predetermined point downstream from the sensor. If the speed of the can line falls, the container sensor and logic associated therewith responds with a certain time delay. In the interim, certain containers may be over or under pressurized with obvious disadvantages.